Answer:
It implies that the defeat of Grendel was strange and mysterious to them but at the same time marvelous, good, and mind-blowing to the Danes.
Step-by-step explanation:
Grendel for several years had terrorized the Danes, killing their men as he wished. Now came the victor Beowulf from Geatland who volunteered to destroy Gendel. He engaged Grendel in a very fierce battle that lasted days until he pierced through him with his sword.
It was unheard of that anyone could actually succeed at eliminating Grendel. So, when Beowulf succeeded at it, it was strange to the Danes but at the same time a welcome development which caused them great joy. They celebrated Beowulf for his victory and King Hrothgar praised him for his courage.